The present invention relates to pen plotters and systems for sensing pen presence and identification of pen type associated therewith and, more particularly, in a graphics pen plotter including a pen gripping mechanism for gripping a cylindrical bodied pen in a generally vertical orientation, to the improvements of the present invention for sensing the presence and type of a pen in the gripping mechanism comprising, a multi-channel sensor including means for producing and sensing a plurality, "n+1", of parallel light beams disposed one above the other to produce a binary number at an output thereof indicating the ones of the light beams sensed by the sensor, the sensor being disposed to shine the light beams at a position past which the pen is moved by the gripping mechanism; and, a cylindrical reflective surface disposed about a portion of the body of the pen so as to be struck by the light beams when the pen is being gripped by the gripping mechanism at the position and reflect the light beams back towards the sensor to be sensed thereby, the reflective surface having "n" cylindrical strip positions disposed to be struck by " n" of the light beams for selectively containing non-reflective strips to indicate a binary indication of the pen type whereby one digit of the binary number output indicates the presence or absence of a pen at the position and the remaining "n" digits of the binary number designate one of 2.sup.n possible pen types.
Modern pen plotters employ a variety of types of pens therein requiring different pen speeds, pen pressures, etc., to create optimum line quality. As a very basic approach, one can provide the plotter with such information prior to the beginning of a plot where a single type of pen is to be employed. Most quality, production grade, commercial plotters, however, employ a multitude of pens even within a single plot for purposes of changing color, line width and the like. Accordingly, it is known in the art to provide each pen with readable indicia so that the pen type can be dynamically determined during the plotting process.
A typical prior art approach to the determination of pen types is shown in FIGS. 1-4. The cylindrical plastic body 10 of each pen 12 is provided with a plurality of strips 14 of reflective tape in a pre-established configuration for each pen type. A sensor system, generally indicated as 16, is used to vertically scan the strips 14 on each pen 12 to determine the pen type. Sensor system 16 comprises a light beam source 18 and a light detector 20 mounted to a moving member 22 so that light 24 striking a strip 14 of reflective tape will be reflected to the light detector 20 to produce a signal on the wires 26. Typically, the source 18 and detector 20 employ modern diode technology; that is, there is a light-emitting diode (LED) within the light beam source 18 and a photo transistor within the light detector 20. The moving member 22 is scanned vertically across the strips 14, as indicated by the arrow 28, by an appropriate mechanism (not shown). Alternatively, of course, the pen 12 could be moved vertically across a stationary sensor to achieve the same results. As those skilled in the art will recognize, if four strips 14 of reflective tape are present at four associated positions on the body 10 of pen 12, the output from the sensor system 16 on wires 26 will be a binary 15, i.e., "1111". By eliminating various ones of the strips 14, the other fifteen possible combinations of four binary bits (i.e., 0000-1110) can be produced. More or less strip positions can, of course, be used as desired for fewer or greater possible numerical designations of type.
The critical portions of interest of a modern pen plotter employing a carousel 30 for holding a plurality of pens is shown in FIG. 4. A pen holder 32 moves back and forth along a support beam 34 within the plotting area 36 when actively plotting. To pick up or change a pen 12, the pen holder 32 moves from the plotting area 36 off station to the carousel 30 as indicated by the dotted arrow 38. To sense pen type, the carousel 30 must be rotated as indicated by the arrows 40 to first position the desired pen 12 adjacent the sensor system 16 wherein it is vertically scanned by sensor system 16 as described above. The carousel 30 is then rotated to place the pen 12 at the pickup position to be picked up by the pen holder 32. As can be appreciated, this is a two-step operation requiring both time and associated logic within the plotting system to accomplish it. Additionally, the sensor system 16 as described above is relatively complex and parts intensive in order to be able to properly vertically scan the strips 14 in the manner previously described.
Moreover, to determine if a pen 12 is in the pen holder 32, a separate sensor (not shown) is typically employed. Thus, there tends to be a redundancy of sensors in the typic
While not incorporated into any commercial pen plotters known to the applicants herein or their assignee, the Japanese Patent Application of Watanabe published in Mar. of 1982 as No. 57-45099 (copy filed herewith) depicts in FIGS. 2 (a) and (b) thereof what appears to be three sensors (84) stacked one above the other in spaced relationship so as to read three corresponding sensible strips (94) on a pen (9). Apparently, the intent is to read the three strip positions simultaneously to develop a binary signal between 000 and 111 (depending on the strips actually present) without the need to scan vertically across the strip positions with a single sensor. A representation of the Watanabe approach as it relates to the drawing of FIGS. 1-3 is shown in FIG. 5 hereof.
Wherefore, it is the object of the present invention to provide a pen plotter pen type identification system which is simple in constructions and which can dynamically scan a pen anywhere throughout its path of movement without the requirement of the pen being moved to a separate sensing location or having to stop.
It is another object of the present invention to provide a pen plotter pen type identification system which produces output sensing with discrete TTL switching signal levels.
It is still another object of the present invention to provide a pen plotter pen type identification system which also provides indication of pen presence employing a single sensor for both purposes.
It is yet another object of the present invention to provide a pen plotter pen which is sensible by a single sensor as to both its type and presence.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter taken in conjunction with the drawings which accompany it.